Dual Homed ISP - BGP for failover - IP Block Routing questions.

The Firewall behind R1 & R2 is setup for failover (Active/Standby). So R1 and R2 have HSRP on their LAN Interfaces - one HSRP Group fro Each ISP.

I have a PUBLIC IP Block, say 4.5.6.0/24, which is being advertized over BOTH R1 & R2, but R1 being a preferred route when both links are active (using AS-Prepend for that IP Block, on R2). Idea is, when R1-ISP1 link Fails, the IP block 4.5.6.0/24 msut be reachable over R2-ISP2 Link (link with a longer AS-Path).

But, when R1-ISP1 link fails, the route for 4.5.6.0/24 does NOT reconverge- The Upstream ISPs (confirmed via a looking glass site)- are still sending traffic over to ISP1, and it dies at R1-ISP1 Link.

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